Dictionary:

energize

  (ĕn'ər-jīz')

1. To give energy to; activate or invigorate: “His childhood—father in . . . prison, factory work as a boy—both haunted and energized him” (Frank Conroy).
2. To supply with an electric current.

To release or put out energy.

verb

To give or impart vitality and energy to (someone or something): exhilarate, invigorate, stimulate, vitalize. See help/harm/harmless.

Definition: activate; give more life
Antonyms: deactivate, debilitate, sap, tire, weaken, weary

Being electrically connected to a voltage source so the device is activated.

The verb has 2 meanings:

Meaning #1: cause to be alert and energetic
  Synonyms: stimulate, arouse, brace, energise, perk up
  Antonym: de-energize (meaning #1)

Meaning #2: raise to a higher energy level
  Synonyms: excite, energise